IMPROVEMENT OF THE HYDRAULIC PROPERTIES OF SALINE-SODIC SOIL EXPOSED TO FREEZING-THAWING USING SEWAGE SLUDGE AND WETTING-DRYING PROCESS WITH WASTEWATER

Soil improvement practices are needed to protect weakly aggregated saline-sodic soils in cold regions from the negative effects of freezing-thawing events. Amelioration of these soils by adding sewage sludge and applying wetting–drying process with wastewater can be a practical application due to aggregation to be increased with increase in organic matter. Therefore, a laboratory experiment has been conducted to determine the effects on soil properties with three stabilized sewage sludge doses (0, 50, 100 Mg ha−1), two freeze-thaw cycles (5 and 10 times), two wetting-drying intervals (4 and 8 days) and two water types (freshwater and recycled wastewater). The negative effects of freezing-thawing on organic matter and aggregate stability were determined. However, while sewage sludge increased organic matter, aggregate stability, salinity, exchangeable K and Ca+Mg contents, cation exchange capacity (CEC), it was instrumental in inducing a lower pH, exchangeable Na, CaCO3 and exchangeable sodium percentage (ESP), and thus improved field capacity and hydraulic conductivity. Wetting-drying with 8-day intervals and wastewater improved organic matter also. Therefore, it could be concluded that the improvement of hydraulic properties can be attributed to achieving better aggregate stability with increased organic matter in soil from sewage sludge. Long intervals of wetting-drying and recycled wastewater can promote good results as well. However, improving the findings with the proposed treatments in the outer field conditions of the regions exposed to freezing-thawing events will provide more practical use.